1. Technical Field
The invention relates to fiber optical devices. More particularly, the invention relates to optical couplers for combining or splitting optical signals using folded waveguides and method for making the same.
2. Description of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. DWDM (Dense Wavelength Division Multiplexing) is one of the key technologies for such optical fiber communication networks. DWDM employs multiple wavelengths or channels in a single fiber to transmit in parallel different communication protocols and bit rates. Transmitting several channels in a single optical fiber at different wavelengths can multi-fold expand the transmission capacity of the existing optical transmission systems, and facilitating many functions in optical networking.
Optical telecommunications generally involves the use of light beams propagating through optical fibers to transmit data from one end to another end. When an optical fiber carrying an input data signal that needs to be connected to two destinations, the signal needs to be split into two parts. This is achieved in the art by a coupler. When used for the splitting purpose, it is often referred to as a splitter. Generally, a coupler is bi-directional. When a coupler is used to combine two signals respectively from two sources, the coupler is used as a combiner to combine the two signals onto a single optical fiber.
FIG. 1 shows a top view of an optical coupler 100 according to a generic design known in the art. In particular, when used as a splitter, the optical coupler 100 has an input port 102 at one end and four output ports 104 at the other end. In operation, an optical signal coming to the input port 102 is coupled into a waveguide 106 that forks into two forking waveguides 108 and 110 or a Y junction element. As shown in the figure, the two waveguides 108 and 110 or are respectively further split into two ending waveguides 112, each coupled to one of the four output ports 104. As a result, the optical signal can be split into four parts, respectively output from the four output ports 104.
One of the problems with the optical coupler 100 is the alignment procedures afterward. In general, an alignment of the input port 102 with respect to a device may need to be performed first, then another alignment of the four outputs 104 with respect to one or more other devices needs to be performed, or vice versa. While many of the alignment procedures are performed manually, this increases the overall costs of such devices. There is thus a need for the devices that can simplify the alignment procedures without significant loss of performance of the devices. In addition, the optical coupler 100 has ports (i.e., input and output ports) on both sides, the resultant footprint of the optical coupler 100 could limit its uses in many situations. There is another need for the devices that can be designed with reduced footprint.
The present invention, generally speaking, pertains to an optical apparatus for combining and splitting optical signals using folded waveguides and method for making the same. According to one aspect of the present invention, at least one waveguide used in the optical apparatus is folded around according to a predefined curve to couple to other waveguides. The predefined curve is so designed as to minimize possible insertion loss as a result of such folding of the waveguide. The proper folding of the waveguide leads to modified designs of the optical devices with all the ports on one side so as to simplify the alignment procedures afterward. In addition, the optical device according to the present invention has much smaller footprint and makes it possible to increase higher yield from fabricating substrate material on which the waveguides are formed.
In one embodiment, a main waveguide is folded in such a way that both ends of the main waveguide are towards the same direction, one end is coupled to a port and the other end forks into or is coupled to two separate waveguides. Each of the two separate waveguides further forks into two separate waveguides. In one application, the optical device is used to combine signals. Several individual signals can thus be merged into the main waveguide from the separate waveguides. In another application, the optical device is used to split a signal. The signal coming out of the main waveguide is split into two signals that can be further respectively split along the separate waveguides.
According to another embodiment having a first port and a set of second ports, a pair of immediate waveguides, at one end, coupled to the main waveguide is folded around two opposite directions, at the other end, to respectively couple to the other waveguides so as balance the second ports around the first port, all are on one side.
One of the objects of the present invention is to provide an effective solutions for designing, configuring, or manufacturing couplers used for either splitting or combining optical signals by bending one or two waveguides properly.